Four month sleep regression suggestions

I had done the Taking Cara Babies newborn class and my baby was sleeping through the night, we hit 17 weeks and his sleep has been a nightmare. His naps last 30 minutes unless I rock him back to sleep and continue to hold him for the rest of the nap and he is up multiple times a night just wanting to be held and cuddled or eat. As soon as I try to lay him back in his crib he starts crying again. Wondering if anyone has any suggestions for how to lengthen naps? And how to get them sleeping through the night again? Does it just happened all of a sudden or should I be doing something more? We are usually up from 1 to 330 rocking him back to sleep then at 3:30 I will feed him then he will go back to sleep for a few more hours then I'll have to rock him back to sleep again for an hour then he'll sleep for a few more hours and then we get up for the day.